| Qingyi River is secondary tributary of the Huai River,70%of the watershed area is located in Xuchang,the sewage discharge has an important influence on the water environment of Qingyi River basin.Xuchang is China's largest hair-products industry gathering area.High water consumption and severe pollution are typical characteristics of the hair-product industry which is one of the major polluting industries in Qingyi River Basin.The COD emission of hair-product industry rank after textile industry and papermaking industry and its nitrogen emission rank second after papermaking industry.Hair-products industrial cluster sewage includes not only wig wastewater,but also other industrial wastewater and residential sewage,characterized by complex composition,instable water quality and water quantity.This article relied on A2/O process adopted by Tunnan Sewage Treatment Plant in industry cluster distinct and conducted laboratory and pilot tests to explore reasonable and optimum condition for wastewater treatment which is of similarity.Meanwhile,theoretical knowledge was applied to practical engineering by means of engineering operation.For the purpose of improving the treatment effect of A2/O process on industry cluster wastewater,the effect and mechanism of pollutants removal were investigated by treating the actual sewage through A2/O reactor.The optimal operating parameters were optimized by adjusting hydraulic retention time(HRT),mixture reflux ratio(R),sludge reflux ratio(r),sludge retention time(SRT)and dissolved oxygen(DO).Furthermore,Na2S2O3 was added to the anoxic zone to investigate the effect of denitrification and dephosphorization and molecular biotechnology was used to analyze the variation of microbial community.The study improved A2/O process by modifying the reactor as“anaerobic-anoxic-aerobic-anoxic" operation mode.In the aspect of advantages and disadvantages of the modified system,pollutants removal effect and their change along the process were analyzed and the variations of microbial community in the activated sludge were compared as well.Based on the results of the tests,this study also carried out a design of A2/O device in pilot scale and observed the effect of pollutant removal under five different operating conditions.The seasonal influence of MLSS and DO on denitrification and dephosphorization were explored on the basis of A2/O wastewater treatment project of Tunnan Sewage Treatment Plant.Main contents are summarized as follows:(1)Optimization tests compared the removal effect under 24h?16h and 10h HRT conditions,which showed that the 1Oh HRT condition was beneficial for phosphorus removal but not conducive to the degradation of COD and the removal of TN.However,the phosphorus removal effect of 24h was less significant than that of 16h,and the removal efficiency of COD and TN was similar.Considering the mixed liquor reflux ratio(R),the conditions were set as 100%,200%and 300%.The results indicated that the change of R had slight impact on the removal of COD,NH4+-N and TP.Corresponding to the increase of ratio,the removal rate of TN promoted from 57.82%to 66.86%and 76.27%,respectively.In sludge reflux ratio(r)comparing tests,the ratio was set as 50%,75%and 100%.Under low range,sludge was trend to deposit in the secondary settling tank and was bad for COD removal.However,in the high range,more NO3--N would be carried into the anaerobic tank thus shock the phosphorus release.On the other hand,along with the increase of ratio,the removal rate of TP present downward trend from 86.11%to 84.41%and 81.88%.The effects of sludge retention time(SRT)on the removal of pollutants at 8 days,11 days,15 days and 20 days were observed later.When SRT was 8d,the removal rate of TP was 91.35%and the removal of COD,NH4+-N and TN behaved badly.The removal effect of TN remained poor under SRT 11d while up to 74.25%and 72.15%under SRT 15d and 20d,respectively.On the contrary,the phosphorus removal rate drop to 56.60%when SRT was 20d.Moreover,the effect of DO on the performance of A2/0 process was studied by setting the concentration of DO at 4.0,3.0,2.0,1.0mg/L.It was observed that the effect of DO on COD removal was invisible,whereas the removal rate of TN increased with the decrease of DO.When the concentration of DO was approximately 1.Omg/L,the efficiency of phosphorus removal deteriorated dramatically.On the whole,in order to achieve excellent nitrogen removal efficiency,the system can be operated under low DO conditions.Ultimately,the optimal operation conditions were determined to be HRT 16h,R 200%,r 75%,SRT 15 d and DO?2.0mg/L.Adding Na2S2O3 for denitrification enhancement was examined,which was found make no difference to the removal of COD and NH4+-N whereas the average removal rate of TN increased from 68.29%to 76.26%.According to change of microbial community,the reason mainly depends on the rapid proliferation of Hydrogenophaga,among which H.tyringiospiralis and H.fseudoflava can utilize nitrates as electron donor for denitrifying under anaerobic conditions.Sulfuritalea can also take advantage of sulfur for denitrification.(2)The removal effects of contaminants at 200%,150%and 100%internal reflux ratio were studied in the modified A2/O reactor.Compared with the traditional A2/O process,the modified A2/O process can lift the rate of denitrification,the nitrogen removal rate increased from 70.45%to about 73.90%in the reflux ratio of 200%.Although the nitrogen removal was not obvious in the post-anoxic zone,the front-anoxic denitrification was enhanced by avoiding internal reflow carrying DO to the front-anoxic zone.The removal efficiency of COD,NH4+-N and TP by the modified A2/O process was approximate to that of the conventional A2/O process.In terms of the microbial community,Thauera propagated rapidly in the modified A2/O system which is a kind of denitrifying bacteria belongs to Rhodocyclaceae.The deterioration of the denitrification effect is closely related to the abundance of Thauera as the ratio of Thauera drop from 19.59%to 5.92%and 6.13%.The population of Comamonadaceae had an edge in the modified A2/O system,which is in favor of shortcut nitrification and denitrification.(3)The pilot tests respectively regulated the hydraulic retention time as 16h,12h and 10h and the internal reflux ratio as 200%and 100%and adjusted MLSS constantly.It turned out that the system exhibited an efficient removal on COD and NH4+-N under each condition.Internal reflux played a more important role in TN removal than HRT.Chemical phosphorus removal technology was required on account of the effluent concentration of PO43--P exceeded 0.5mg/L all the time.By virtue of the A2/O process of Tunnan Wastewater Treatment Plant in Xuchang,the interaction between MLSS and DO was investigated from season to season,coming out that MLSS in summer was significantly lower than in winter and excessively high MLSS would give rise to DO decline and negatively affected COD and NH4+-N removal at the moment between Winter and Spring with the rise in temperature.The removal of PO43--P was mainly through the combination of biological and chemical methods,which ensured that the effluent phosphorus concentration meets the emission standard stably. |
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